The place where a vehicle tire directly interfaces with a road or other driving surface is often referred to as the contact area. The size, shape, and related dynamics of the contact area, or “footprint,” of each tire on a vehicle can provide important information about vehicle size and load, tire pressure and characteristics, road surface, operating and driving conditions, and other factors. Accordingly, detecting and monitoring the footprint during vehicle operation can provide valuable information for improving vehicle handling and safety.
In the past, tire footprints have been measured quasi-statically using pressure sensitive devices positioned between the tire and the driving surface. These devices use capacitive or photo/print techniques in order to image the contact area. Specially prepared transparent inserts in the road in conjunction with optical detection methods have also been used. While successful at identifying the footprint, practical use of these methods is limited because they cannot measure the footprint and determine related contact information during real driving conditions.
Other methods that use multiple sensors inside the tire for continuous measurement of the footprint have also been proposed. A potential disadvantage with such methods as they currently exist is a more complicated implementation of these sensors and the need for advanced data analysis due to high bandwidth and data rates. Further, sensors in the tire(s) need an independent power supply, typically a battery, which limits the energy available for data processing and transmission of data out of the tire by radio frequency (RF) communications. Additionally, the overall weight of these sensors, as well as their power supplies and other system components, is often required to be below five grams in order to fulfill original equipment manufacturer (OEM) requirements, which can limit system design.